This application claims priority to application number 02157220.8, filed Dec. 20, 2002 in the People""s Republic of China.
The present invention relates to processing pigskin, which skin is used to make such products such as pet (animal) chews and treats.
Dog treats and chews are given to dogs for a variety of reasons. Dog chews are used to help clean the teeth of dogs. Dog treats may have the same cleaning function, as well as provide nutritional value.
Many dog chews are made from rawhide, which is untanned cow skin. The skin is dehaired and cleaned of fat and muscle. The rawhide may be bleached with hydrogen peroxide to improve its appearance. The skin is then manipulated into the desired shape, such as by folding or rolling, and dried.
The problem with rawhide is that it is indigestible, being essentially leather. Dogs lack the enzymes needed to digest the rawhide. When a dog chews rawhide, pieces can break off and lodge in the dog""s digestive tract. In some cases, an occlusion, or blockage, as well as impaction, occurs, requiring veterinary attention. Furthermore, rawhide is low in palatability, so that dogs quickly lose interest in it.
An alternative to rawhide chews and treats are pigskin products. Pigskin is digestible and has some nutritional value. Pigskin stimulates the dog""s gastrointestinal tract to produce digestive enzymes. Thus, pieces that enter the digestive tract of dogs do not cause problems.
Furthermore, pigskin is generally used for other products other than pet chews and treats. The production of leather creates leftovers or scrapes of skin that can be used for colloidal protein and for making pet supply products.
Untanned pigskin is so unsightly that humans are unlikely to purchase products made from it. In order to increase the visual attractiveness of dog chews and treats, the pigskin product is smoked. Smoking imparts a browning color to the skin. Unfortunately, smoking increases the acidity of the product, thereby reducing its palatability to dogs. The product may be coated with molasses or other things to alleviate the smoke flavor, but these coatings are easily licked off because the coating does not penetrate the skin product. The remaining product is then discarded by lack of interest by dogs.
In addition, pigskin is different from rawhide so that some of the processes used for rawhide do not work well for pigskin. Pigskin contains oils and impurities not found in rawhide and the skin fiber is different.
Thus, what is needed is a pigskin suitable for use in dog products, which pigskin is both attractive to humans and palatable to dogs.
The present invention provides a method of processing pigskins having a moisture content of 50-80% by weight. The skin is processed with a lime alkali paste. The paste is applied to the skins to dissolve colloidal protein therein. The paste comprises an alkali liquid, alkali enzymes and lime, with the paste having a pH of greater than or equal to 12. The skins are washed in ammonium chloride or chloride sulphate and then the skins are cleaned in water. The skins are washed in ammonium chloride or chloride sulphate and in enzymes to soften the skins. The fat is removed from the skins and the skins are bleached with hydrogen peroxide or potassium permanganate.
In accordance with one aspect of the present invention the step of applying a paste to the skins further comprises the step of applying a paste comprising a concentration of alkali liquid of 10-30% by weight of sodium sulfide, lime and 0.01-0.05% by weight of alkali enzymes and applying the paste to the skins for 10-30 hours.
In accordance with another aspect of the present invention the step of washing the skins in ammonium chloride or chloride sulphate further comprises the step of washing the skins in 1-2.5% by weight of ammonium chloride for 0.5-3 hours.
In accordance with still another aspect of the present invention, the step of washing the skins in ammonium chloride or chloride sulphate, and in enzymes, further comprises the step of washing the skins in 4-8% by weight of ammonium chloride and 0.1-0.5% by weight of pancreatic enzymes for 3-8 hours.
In accordance with still another aspect of the present invention, the step of bleaching the skins with hydrogen peroxide or potassium permanganate further comprises the step of washing the skins in 15-30% by weight of hydrogen peroxide for 0.5-5 hours.
In accordance with another aspect of the present invention the processed pigskins are expanded, white and soft.
The present invention also provides a method of treating pigskins, comprising the steps of applying an alkali paste to the skins to dissolve colloidal protein in the skins. The alkali is removed from the skins. The skins are washed with pancreatic enzymes so as to soften the skins. Fat is removed from the skins. The skins are washed with a bleaching agent so as to whiten and expand the skins.
In accordance with one aspect of the present invention the step of applying an alkali paste further comprises the step of applying an alkali paste comprising an alkali, an alkali enzyme and lime, the paste having a pH of greater than or equal to 12.
In accordance with another aspect of the present invention the step of applying an alkali paste further comprises the step of applying an alkali paste comprising 10-40% by weight of an alkali liquid, 0.01-0.05% by weight of an alkali enzyme and a quantity of lime to raise the pH to greater than or equal to 12.
In accordance with another aspect of the present invention the step of removing the alkali from the skins further comprises the step of washing the skins in at least one of the group consisting of ammonium chloride, ammonium sulfide and chloride sulphate.
In accordance with still another aspect of the present invention the step of removing the alkali from the skins comprises at least two washes and the step of washing the skins with pancreatic enzymes occurs simultaneously with one of the washes to remove the alkali from the skins.
In accordance with still another aspect of the present invention the step of removing fat from the skins further comprises the step of washing the skins in a surfactant.
In accordance with still another aspect of the present invention the step of washing the skins with a bleaching agent further comprises the step of washing the skins with 15-30% by weight of hydrogen peroxide.
In accordance with still another aspect of the present invention the following steps are performed, before applying the alkali paste to the skins. The skins are wetted with lime liquid and an outside layer of the skins is removed and the inner layers are retained.
In accordance with still another aspect of the present invention, after washing the skins with a bleaching agent, the wet skins are formed into pet chew products and the products are dried.
In accordance with still another aspect of the present invention, the skins are swelled by wetting the skins with lime liquid and the skins are expanded by baking the bleached skins.
The present invention also provides an animal chew that comprises pigskin shaped into a chew product. The pigskin has its colloidal protein removed, the pigskins is soft when wet, the pigskin is bleached and the pigskin is expanded relative to raw pigskin.
In accordance with one aspect of the present invention the pigskin is made soft when wet due to being treated with pancreatic enzymes.
In accordance with another aspect of the present invention the pigskins comprise the inner layer of a pig""s hide.